Relationships between ovarian blood flow and ovarian response to eCG-treatment of dairy cows

The goal of the present study was to investigate ovarian blood flow and ovarian response in cows undergoing a gonadotropin treatment to induce a superovulatory response, using transrectal colour Doppler sonography. Forty-two cows including 19 cross-bred, 14 German Holstein and 9 German Black Pied cows were examined sonographically before hormonal stimulation on Day 10 of the oestrous cycle, three days after administration of eCG (Day 13) and seven days after artificial insemination (Day 7p.i.). After each Doppler examination, blood was collected for determination of total oestrogens (E) and progesterone (P₄) in peripheral plasma. The blood flow volume (BFV) and pulsatility index (PI), which is a measure for blood flow resistance, were determined in the ovarian artery, and B-mode sonography was used to count dominant follicles and corpora lutea. Important criteria to assess the ovarian response following the hormonal treatment were the number of follicles >5mm in diameter on Day 13 and the number of corpora lutea on Day 7p.i. per cow. The number of follicles ranged from 2 to 61 (mean±S.E.M.: 17.5±1.7) and corpora lutea from 0 to 50 (mean±S.E.M.: 17.0±1.6). The BFV increased from 28.4 to 45.0ml/min between Days 10 and 13 and reached a maximum of 108.5ml/min on Day 7p.i. The PI decreased from 6.25 on Day 10 to 4.70 on Day 13 and to 2.10 on Day 7p.i. The BFV and PI on Day 13 did not correlate with the number of follicles (P >0.05). However, on Day 7p.i. the number of corpora lutea correlated positively with the BFV (r =0.64; P <0.0001), and an inverse relationship was found for the PI (r =-0.51; P =0.0005). There were no correlations (P >0.05) between the BFV and PI on Day 10 and the number of follicles on Day 13 or the number of corpora lutea on Day 7p.i. Results of the present study show that in cows, a hormonal treatment to induce a superovulatory response yielded a marked increase in BFV and a marked decrease in PI in the ovarian artery. However, there was no correlation between BFV and PI in the ovarian arteries before hormonal stimulation and the number of follicles and corpora lutea that developed after stimulation. Thus BFV and PI measured in the ovarian arteries have limited diagnostic value to predict the outcome of a gonadotropin treatment.